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Author Topic: Rcvr- learn from my mistake!  (Read 4030 times)
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Carl WA1KPD
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« on: February 02, 2011, 04:29:25 PM »

Duh

Reading Bruce's comment about gratification from finding a problem in a rig (re. HQ-129 xtal filter)  made me decide to share this story

This fall I picked up a very nicely done HB rcvr circa 1940s. It uses the RF/Mixer/Osc package with slide rule dial and band spread that you could purchase as a package from Meissner.  There is no documentation but by doing a careful recaping, and replacement of the one out of spec resistor, I brought it back to life. I also had to firqure out how to restring the main tuning and bandspread as both were broken and in pieces. All of this took from Thanksgiving to now.

At any rate for more hours than I want to admit I have been struggling with the alignment of the Meissner section. Almost every trimmer and padder in the osc section had to be screwed down all the way and it was still reading high. Since each band has an independent Osc coil and adjustments that are switched out, I was at a loss as to where the problem could lie. The only common element was the main tuning caps which I had not touched.

Reading my Marcus and Levy book in bed one night something struck me and I got up and went into the shop to check it out.........

If you want to guess what the problem was I'll provide the answer in a response. It was so simple and so basic I had to laugh at myself. Sometimes you cannot see the forest for the trees.

 It has some quirks that I have not figured out yet  and needs a little more attention. May they all be as simple as this.

Carl

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Carl

"Okay, gang are you ready to play radio? Are you ready to shuffle off the mortal coil of mediocrity? I am if you are." Shepherd
Carl WA1KPD
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« Reply #1 on: February 02, 2011, 04:33:03 PM »

In all my work the main tuning slide rule pointer had shifted about 1/2 an inch to the right. So when the cap was fully open it was off the scale. I should have realized that every band was missing alignment by 1/2 an inch. Instead I just saw the freq differential increasing with each band and "Ass U ME D" it was a problem with the oscillator.

Carl
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Carl

"Okay, gang are you ready to play radio? Are you ready to shuffle off the mortal coil of mediocrity? I am if you are." Shepherd
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« Reply #2 on: February 02, 2011, 10:18:17 PM »

Doh!!!! Good catch Carl!
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W1UJR
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« Reply #3 on: February 02, 2011, 10:31:32 PM »

What a great story Carl!
I can share your pain....and your joy.

I too suffered from my share of those "Ass U Me D" moments....and suffered from the most painful bite of the "Ass U Me D" monster.  Wink I'm now a member of AAA Anti-Assumers Anonymous.

My Worse - For over a year my HRO 5 standing monitoring duty on the workbench seemed to be intermittently deaf, would work great for hours only to have signals almost fade away. Ah ha, bad caps I said, one of its 70 year old paper caps was breaking down with heat...replaced them all...played well for awhile, then back came the problem...ok, not a bad cap, must be a bad resistor....set on its side, bottom cover off, Simpson 260 lashed into circut...could never get it to act up with the meter at hand...

Ok, its got to be a bad tubes...yea, thats it, putting it on its side with the bottom cover off increased air flow and the tubes were not acting up...or so I assumed...sure that is the problem...one of those 70 year old tubes was weak or gassy and not showing up on my trusty Hicock tube tester....replaced them all....still the problem remained, would work for 10 minutes sometimes, or even hours or days, but without warning the signals would fade away, still there, but much, much weaker. Of course it was a pretty set, why does all the ratty looking gear work well, and the very clean gear always be so temperamental..oh, those women are like radios thoughts again...

Only a year and countless hours later did I discover that the MFJ antenna switch connected to the workbench had developed an internal problem, the solder connection on one of the SO-239 connectors was cracked, and the connector was afloat in switch. Poor design, rather than bolting in, the connector was just pressed into the switch body and it had worked loose, stressing and opening up the solder joint sporadically. I finally understand what I've heard folks share MFJ really stood for. Of course it worked fine on the other three posistions which fed the rest of the station, only the workbench outlet had a problem...

Where can those insights come from during those WOW moments...other than our brain idling away on a problem...amazing how well those God given computers really work!

Tnx for sharing OM.

-Bruce

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« Reply #4 on: February 03, 2011, 09:12:26 AM »

I'm sure EVERYONE that messes with this old stuff has been bitten more than once by a simple but overlooked problem. I know I have on several occasions. After spending countless hours futzing with something, (and inventing at least a dozen new cusswords) when you are just about to give it "flying lessons" You trip over the problem. A few more choice cusswords and you sit back and laugh at yourself for overlooking it. If it bites you in the a$$ hard enough, you will never forget to look there again!  Grin  Grin Been there, done that!  Grin  Grin

The worst one I ever had was a deaf SX-17!! I picked it up partially dissassembled inthe name of restoration. The previous owner had snipped out most of the caps and resistors but everything else was intact, and it looked good cosmetically. I replaced all (that I noticed  Wink ) of the missing components. After about 100 hours of bench time It played, the dial tracked perfectly, but it was friggin DEAF! !

I did all of the usual voltage checks and all seemed well. I could not easily get to the bottom of the mixer tube socket, though. I figgered it was ok since it "seemed" to be working. Stage gain checks of the audio and IF sections were good, but it was DEAF.

I was so frustrated that I was going to take it outside, open up the trap door, pour some gasoline in it and light it. Then take a picture of it with the flames coming out of the top and post it here. Calling it "One Hot Receiver".

I finally decided to find a way to check the voltages at the mixer tube. I dont like to use them in RF circuits, but I grabbed an octal tube extender, and all became very clear..................... No screen voltage on the mixer tube. AHA!! Well..............
The screen dropping resistor for the mixer was supposed to be on the total opposite side of the chassis. And it was not there!! It had been clipped out by the previous owner and I missed it!! Bitten again! I HAD BEEN HAD! !!! !   One resistor later it came to life and played fantastic!!

Everytime Vortex Joe would come over my house, he would drool over it. So, one day I unhooked it, handed it to him, and told him to take it home with him!!
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